Synthesis and characterization of sterically hindered arylsilanes containing the 2,4,6-trimethoxyphenyl ligand (TMP): X-ray structures of (TMP)SiH3, (TMP)2SiH2, and (TMP)3SiH

Article abstract of DOI:10.1016/S0022-328X(99)00345-9

The homologous series of primary, secondary and tertiary silanes containing the sterically demanding 2,4,6-trimethoxyphenyl (TMP) group have been prepared in yields ranging from 22 to 45%. The arylsilanes were characterized by multinuclear NMR, IR, GC-MS,

Full text of DOI:10.1016/S0022-328X(99)00345-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 588 (1999) 51–59
Synthesis and characterization of sterically hindered arylsilanes
containing the 2,4,6-trimethoxyphenyl ligand (TMP): X-ray
structures of (TMP)SiH3, (TMP)2SiH2, and (TMP)3SiH
Janet Braddock-Wilking *, Yanina Levchinsky, Nigam P. Rath
Department of Chemistry, Uni6ersity of Missouri–St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA
Received 9 April 1999
Abstract
The homologous series of primary, secondary and tertiary silanes containing the sterically demanding 2,4,6-trimethoxyphenyl
(TMP) group have been prepared in yields ranging from 22 to 45%. The arylsilanes were characterized by multinuclear NMR, IR,
GC–MS, elemental analyses, and X-ray crystallography. Relatively short intramolecular distances are observed between Si and
the O atoms in the ortho-methoxy groups of the aryl ligand and are shorter than the sum of the van der Waal’s radii in the solid
state for all three arylsilanes. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Silicon; Arylsilane; Steric hindrance; Solid state structure
enhanced reactivity of the SiꢀH bond compared with
that of normal hydrosilanes [3]. Herein, we report the
synthesis, spectroscopic and X-ray crystal structure de-
termination of (TMP)SiH3 (1), (TMP)2SiH2 (2), and
(TMP)3SiH (3).
1. Introduction
Sterically hindered ligands are known to stabilize
coordinatively unsaturated molecules, especially those
involving main group elements [1]. In addition, the
steric encumbrance provided by such groups can result
in unusual bonding environments. Recently, we re-
ported the synthesis and characterization of a number
of sterically hindered diarylsilanes containing Mes
(Mes=2,4,6-trimethylphenyl) and RF (RF=2,4,6-
tris(trifluoromethyl)phenyl) substituents [2]. The latter
system exhibited unusual intramolecular interactions in
the solid state.
In a continuation of our study of sterically hindered
arylsilanes, we have prepared mono-, di-, and triarylsi-
lanes containing the bulky and electron-rich 2,4,6-
trimethoxyphenyl (TMP) substituent. The TMP ligand
contains O-donor atoms attached at the ortho-position
of the aromatic ring and provides the potential for
intramolecular interactions. Hydrosilanes containing
substituents that participate in intramolecular interac-
tions with the Si center are of interest, especially in the
2. Results and discussion
Hydrosilanes are synthetically useful precursors for
the preparation of other silicon compounds such as
halosilanes [4], transition metal silyl complexes [5], and
oligo- and polysilanes (through transition-metal-cata-
lyzed dehydrocoupling) [6]. Unfortunately, not very
many sterically demanding hydrosilanes (primary, sec-
ondary, or tertiary) are commercially available but they
can be prepared by relatively simple synthetic
procedures.
Significant interest has been expressed in the use of
the 2,4,6-tris(trifluoromethyl)phenyl group (RF) as a
sterically demanding group for the stabilization of low-
valent main group compounds [7]. The RF ligand pro-
vides a unique blend of stabilizing features: steric
shielding, electron-withdrawing capability due to the
CF3 groups, and electron-donating ability via the lone
pairs on the fluorine atoms in the ortho-CF3 positions.
* Corresponding author. Tel.: +1-314-5166436; fax: +1-314-
5165342.
E-mail address: wilking@jinx.umsl.edu (J. Braddock-Wilking)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00345-9

52
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
A related sterically hindered aryl group capable of all
of the stabilizing features found with the RF but with
electron-donating groups can be found in the 2,4,6-
trimethoxyphenyl substituent (TMP). This ligand
should have roughly the same steric size as the RF and
mesityl groups but is more electron-rich as illustrated
by the triarylphosphine P(TMP)3 which is a highly
basic phosphine due to the presence of the TMP sub-
stituents [8].
amount of (TMP)H was formed (probably due to cleav-
age of the TMP group at silicon by LiAlH4) making the
separation of the starting material from (TMP)SiH3
easier. An analytical sample of (TMP)SiH3 was ob-
tained by repeated fractional crystallization. The use of
SiCl4 for the preparation of either (TMP)2SiH2 or
(TMP)3SiH was unsuccessful. In contrast to the Mes
and RF systems [2], attempts to make H3Si(TMP) from
H3Si(OTf) and (TMP)Li resulted in exclusive formation
of (TMP)H.
1
The SiꢀH resonance in the H-NMR spectrum for
2.1. Synthesis of 2,4,6-trimethoxyphenyl-substituted
compounds 1–3 appear at increasing frequency as aryl
substitution at silicon increases with resonances at l
4.59, 5.61, and 6.36 ppm (C6D6) for 1, 2, and 3,
respectively [11]. A positive shift is also seen in the
29Si{1H}-NMR spectrum for increased aryl substitution
in compounds 1–3: l −80.0 for 1, −67.6 for 2, and
−54.7 ppm for 3. The presence of the SiꢀH unit in 1–3
is also confirmed by the medium to strong SiꢀH stretch-
ing bands near 2200 cm−1 in the infrared spectrum.
In order to optimize yields, several experiments were
performed to determine the best conditions for the
preparation of (TMP)Li from deprotonation of
(TMP)H by n-BuLi followed by quenching with
CD3OD to give (TMP)D. Three different solvents
[DME, Et2O (reflux for 24 h only), and THF] were
employed at room temperature or at reflux from 2–24
h. Analysis by 13C-NMR and mass spectrometry (EI)
showed that the highest yield of (TMP)D was obtained
at room temperature in THF or DME after 2 h (94%)
[12]. Van Koten and coworkers observed by NMR
spectroscopy exclusive formation of (TMP)D [from
(TMP)H and n-BuLi in Et2O for 70 h at room tempera-
ture followed by quenching with D2O] [9a]. In contrast
to the high yields obtained by these authors, only minor
yields of products were obtained in Et2O at room
temperature in the current study.
hydrosilanes
Compounds 1–3 were prepared by the synthetic
route shown in Scheme 1. Direct metallation of 1,3,5-
trimethoxybenzene with n-BuLi (in THF or DME)
afforded the aryllithium reagent, (TMP)Li [9]. Reaction
of the appropriate number of equivalents of (TMP)Li
with HSiCl3 in Et2O provided the intermediate chlorosi-
lanes. The mono- and diarylchlorosilanes were reduced
with LiAlH4 (in Et2O) to provide the desired
hydrosilane.
Compounds 1–3 were isolated as white crystalline
solids in yields ranging from 22 to 45% after an
aqueous workup. Recrystallization from either Et2O or
Et2O/pentane solutions provided X-ray-quality crystals
of 1–3. In addition, compounds 1–3 were characterized
by multinuclear NMR, IR, mass spectrometry and
elemental analyses. A summary of the H and 29Si{1H}
chemical shifts, and SiꢀH stretching frequencies (IR),
melting points, and analyses data, for 1–3 is given in
Table 1.
1
In all the reactions using HSiCl3, a significant
amount of (TMP)H was always observed. This is a
notable problem for the synthesis of (TMP)SiH3 since
these two compounds are difficult to separate from
each other due to similar GC retention times and
solubilities. The formation of large amounts of
(TMP)H is believed to be due to reaction of (TMP)Li
with the acidic proton in HSiCl3 [10]. Compound 1 was
obtained in a slightly higher yield when prepared from
SiCl4 and (TMP)Li followed by reduction with LiAlH4.
Unlike the reaction using HSiCl3 as the silicon precur-
sor, the reaction with SiCl4 displayed a number of color
changes (source not identified). However, a smaller
2.2. X-ray crystal structure analysis of compounds 1–3
The structures of 1–3 were confirmed by single-crys-
tal X-ray diffraction. The molecular structures along
with the atom-numbering scheme are shown in Figs.
1–3, respectively and selected bond lengths and angles
are given in Table 2. Selected nonbonded O···Si···O
Scheme 1.

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
53
Table 1
Selected spectroscopic data, melting points, and elemental analyses for 1–3
b
1H-NMR (l, ppm) a
29Si-NMR (l, ppm) a
−80.0
IR (w, SiꢀH, cm−1
)
m.p. (°C)
Elemental analysis
(TMP)SiH3 (1)
(TMP)2SiH2 (2)
(TMP)3SiH (3)
3.28 (s, o-CH3O)
3.33 (s, p-CH3O)
4.59 (1JSiꢀH=203 Hz)
6.00 (s, ArꢀH)
3.35 (s, o-CH3O)
3.36 (s, p-CH3O)
5.61 (1JSiꢀH=208 Hz)
6.08 (s, ArꢀH)
2192.0,
2155.1
52−54
Calc.
C, 54.51; H, 7.12
Found
C, 54.53; H, 7.09
Calc.
C, 59.31; H, 6.64
Found
C, 58.98; H, 6.51
Calc.
C, 61.11; H, 6.46
Found
−67.6
−54.7
2189.9,
2160.8
105–107
172–174
3.28 (s, o-CH3O)
3.40 (s, p-CH3O)
6.13 (s, ArꢀH)
2169.0
6.36 (1JSiꢀH=221 Hz)
C, 61.06; H, 6.40
a C6D6; 13C-NMR and EI-MS data are found in Section 3.
b KBr pellet.
angles are listed in Table 3 and the structure refinement
parameters and final residual values for 1–3 are listed
in Table 4. Each compound exhibits approximately
tetrahedral coordination at silicon. The SiꢀC bond dis-
tances for 1–3 are close to the mean value in the
Cambridge Structural Database (CSD) for Siꢀaryl
shorter than the sum of the van der Waal’s radii (3.62
,
A) [17] but significantly longer than a typical covalent
,
SiꢀO distance (1.67 A) [18]. The Si···O distances in 1–3
,
all fall in the range of 2.86–3.13 A. Each (TMP) ligand
attached to silicon exhibits one short and one longer
Si···O interaction from the ortho-OMe groups with O
atoms roughly over faces or edges. A similar trend was
seen in the structures of (RF)2Si(H)F [2] and (RF)2SiF2
[2,19] where fluorines from the ortho-CF3 groups on the
aryl ring were found to exhibit short intramolecular
interactions with the silicon center. Each fluorine was
found to occupy a face of the tetrahedron resulting in a
(4+4) coordination environment, which approaches a
distorted tetracapped tetrahedron, similar to bis[2,6-
(dimethylaminomethyl)]silane [20]. Each aryl group dis-
played one short and one longer Si···F separation from
,
bonds found in a number of structures (1.88 A, range
1.83–1.92). A CSD search on the general formula
ArSiH3 (Ar=aryl with any substituent) revealed six
structures, 19 for Ar2SiH2, and 11 for Ar3SiH. To our
knowledge this is the first structural study for a ho-
mologous series of primary, secondary and tertiary
silanes where the aryl groups remain the same.
A slight increase in the SiꢀC bond distance is ob-
,
served when going from 1 (1.863 (2) A) to 3 [1.870
,
(4)–1.880 (3) A], possibly due to the increased steric
hindrance of three aryl groups. The CꢀSiꢀC bond an-
gles range from 109 to 115° in compounds 2 and 3 and
are within the range observed for other secondary and
tertiary silanes. For example, bis(8-(dimethylamino)-
naphthyl)silane [13] displays a CꢀSiꢀC angle of 108°
and the related tertiary silane, tris(8-(dimethylamino)-
naphthyl)silane [14] exhibits three different CꢀSiꢀC an-
gles in the range of 105–108°. Examination of the unit
cells for 1–3 shows notable p-stacking of the aryl
groups. In addition, a propeller arrangement of the aryl
groups in 3 can be seen from Fig. 3. This arrangement
is also found in other triarylsilane structures such as
tris(8-(dimethylamino)naphthyl)silane,
[14]
tris(2-
(dimethylamino)phenyl)silane, [15] and triphenylsilane
[16].
Compounds 1–3 exhibit short intramolecular dis-
tances between silicon and the oxygen atoms in the
ortho-methoxy groups. Fig. 4 shows the local environ-
ment at silicon for compounds 1–3, and the nonbonded
Si···O distances, respectively (covalent bonds are shown
by solid lines and nonbonding interactions are desig-
nated by a dashed line). The Si···O separations are all
Fig. 1. Molecular structure of (TMP)SiH3 (1) showing the atom-label-
ing scheme and 50% thermal ellipsoids.

54
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
2.3. Conclusions
The syntheses of the bulky arylsilanes, (TMP)nSiH4−n
[n=1 (1), 2 (2), or 3 (3); TMP=2,4,6-trimethoxy-
phenyl] have been performed by coupling reactions
using aryllithium reagents and trichlorosilane followed
by reduction with lithium aluminum hydride. However,
in the case of 1, cleaner reaction mixtures were ob-
tained from SiCl4 and (TMP)Li. The arylsilanes were
characterized by 1H-, 13C-, and 29Si-NMR spec-
troscopy, IR, MS, X-ray crystallography, and elemental
analysis. The X-ray structures for compounds 1–3 re-
veal relatively short intramolecular distances between
the oxygen atoms in the ortho-OMe groups on the
aromatic ring and the silicon center. The crystallo-
graphic data suggests that there is no direct interaction
and that the short Si···O distances are a consequence of
the geometrical constraints of the TMP ligand. This is
the first reported structural study of a homologous
series of arylꢀhydrosilanes. Further studies are planned
to explore the utility of these silanes in oxidative addi-
tion reactions to electron rich metal centers and in some
selected cases as precursors to multiply bonded silicon
species.
Fig. 2. Molecular structure of (TMP)2SiH2 (2) showing the atom-
labeling scheme and 50% thermal ellipsoids.
one fluorine at each o-CF3 group, analogous to the
trend seen in the current study. In addition, short
intramolecular E···F interactions were found in divalent
E(RF)2 compounds (E=Ge, Sn, Pb) [21], in
(RF)2MꢀM(RF)2 and (RF)3M (M=In, Ga) [22].
The bond angles at the oxygen atoms in the ortho-
OMe groups in 1–3 might suggest that they are pulled
in towards the silicon atoms (see Table 2), however, the
same trend in the angles is seen for the para-OMe
substituents. In addition, little change is observed in the
Si···O and SiꢀH distances in 1–3. If significant extended
coordination were present the Si···O and SiꢀH distances
would be expected to lengthen through the sequence
1–3. Therefore, it is unlikely that the shortened in-
tramolecular Si···O distances in 1–3 involves a direct
interaction but is probably due to constraints of the
TMP ligand itself.
3. Experimental
All reactions were performed under an Ar atmo-
sphere using standard Schlenk techniques. Diethyl
ether, THF (pre-distilled from CaH2) and 1,2-
dimethoxyethane
(DME)
were
distilled
over
Naꢀbenzophenone ketyl under N2. Trichlorosilane and
SiCl4 were distilled over K2CO3 before use. Benzene-d6
and CDCl3 were obtained from Cambridge Isotopes
Labs, Inc. and were used as received. 1,3,5-Trimethoxy-
benzene, n-butyllithium, and lithium aluminum hydride
are commercially available and were used as received.
1H-, 13C-, and 29Si-NMR spectra were obtained on a
Bruker ARX-500 MHz NMR spectrometer at frequen-
cies of 500, 125, and 99 MHz, respectively using a
5-mm BB tunable probe. Proton and carbon NMR
spectra were referenced to benzene (7.15 and 128.00
ppm, respectively) and silicon spectra were referenced
to external TMS (0 ppm).
Infrared data were collected on a Perkin–Elmer 1600
Series FT-IR. GC analyses were carried out on a
Hewlett–Packard Series II 5890 gas chromatograph
using a DB-5 capillary column and GC–MS data were
collected on
a Hewlett–Packard 5899A GC–MS
equipped with a RTE-A data system. Melting points
were obtained on an Electrothermal 9100 capillary
melting point apparatus and are uncorrected. Micro-
analyses were performed by Schwarzkopf Microanalyti-
cal Laboratory (Woodside, NY) or Atlantic Microlab,
Inc. (Norcross, GA). HR-MS (EI) data were obtained
Fig. 3. Molecular structure of (TMP)3SiH (3) showing the atom-label-
ing scheme and 50% thermal ellipsoids.

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
55
Table 2
Selected bond distances and angles for 1–3
(TMP)SiH3 (1)
(TMP)2SiH2 (2)
(TMP)3SiH (3)
,
Bond distances (A)
SiꢀC1
1.863 (2)
SiꢀC1
SiꢀC10
1.869 (2)
1.869 (2)
SiꢀC1
1.870 (2)
1.877 (2)
1.880 (3)
1.382
SiꢀC10
SiꢀC19
SiꢀH1
SiꢀH1
SiꢀH2
SiꢀH3
1.39 (2)
1.40 (3)
1.42 (3)
SiꢀH1
SiꢀH2
1.389
1.404
Bond angles (°)
O1ꢀC2ꢀC1
O1ꢀC2ꢀC3
O3ꢀC6ꢀC1
O3ꢀC6ꢀC5
O2ꢀC4ꢀC5
O2ꢀC4ꢀC3
115.4 (2)
121.8 (2)
114.4 (2)
123.2 (2)
114.7 (2)
123.5 (2)
O1ꢀC2ꢀC1
O1ꢀC2ꢀC3
O3ꢀC6ꢀC1
O3ꢀC6ꢀC5
O2ꢀC4ꢀC3
O2ꢀC4ꢀC5
O4ꢀC15ꢀC10
O4ꢀC15ꢀC14
O5ꢀC11ꢀC10
O5ꢀC11ꢀC12
O6ꢀC13ꢀC12
O6ꢀC13ꢀC14
115.0 (2)
123.1 (2)
113.7 (2)
123.0 (2)
115.0 (2)
123.6 (2)
114.0 (2)
122.6 (2)
115.3 (2)
122.3 (2)
114.5 (2)
124.0 (2)
O1ꢀC2ꢀC1
O1ꢀC2ꢀC3
O3ꢀC6ꢀC1
O3ꢀC6ꢀC5
O2ꢀC4ꢀC5
O2ꢀC4ꢀC3
113.5 (3)
121.6 (4)
114.9 (4)
123.3 (4)
115.5 (4)
123.3 (5)
115.8 (4)
121.1 (4)
115.7 (5)
123.3 (5)
113.8 (3)
122.9 (4)
115.1 (3)
122.6 (3)
113.7 (3)
124.3 (4)
115.0 (3)
121.2 (3)
112.5
O4ꢀC11ꢀC10
O4ꢀC11ꢀC12
O5ꢀC13ꢀC14
O5ꢀC13ꢀC12
O6ꢀC15ꢀC10
O6ꢀC15ꢀC14
O7ꢀC20ꢀC19
O7ꢀC20ꢀC21
O8ꢀC22ꢀC23
O8ꢀC22ꢀC21
O9ꢀC24ꢀC19
O9ꢀC24ꢀC23
C1ꢀSiꢀC10
C10ꢀSiꢀC19
C1ꢀSiꢀC19
C1ꢀSiꢀH
C1ꢀSiꢀC10
113.55 (8)
115.3
109.3
109.0
103.0
C1ꢀSiꢀH1
C1ꢀSiꢀH2
C1ꢀSiꢀH3
112.0 (10)
112.0 (11)
110.7 (11)
C1ꢀSiꢀH1
C1ꢀSiꢀH2
C10ꢀSiꢀH1
C10ꢀSiꢀH2
H1ꢀSiꢀH2
110.1
109.4
110.6
109.9
102.8
C10ꢀSiꢀH
C19ꢀSiꢀH1
107.4
H1ꢀSiꢀH2
H1ꢀSiꢀH3
H2ꢀSiꢀH3
107 (2)
110.0 (14)
104 (2)
from The Washington University High Resolution
Mass Spectrometry Facility.
the solid dissolved in 50 ml of Et2O and then added
dropwise to a slurry of LiAlH4 (1.21 g, 32 mmol) in 75
ml of Et2O. The reaction mixture was heated to reflux
for 12 h. After an aqueous workup with saturated
NH4Cl, the organic layer was extracted with Et2O and
dried over anhydrous Na2SO4. After removal of the
solvent, the product was purified by Kugelrohr distilla-
tion and fractional crystallization providing a white
solid (crude yield), 2.45 g, 45% (95% purity by GC).
Attempts to remove the by-product (TMP)H by
column chromatography and preparative GC failed. A
pure sample of 1 was obtained by repeated fractional
crystallization from pentane–Et2O (1:1). Spectroscopic
data for 1: 13C{1H}-NMR (C6D6): l 55.03 (p-OMe),
55.39 (o-OMe), 91.04 (m-ring carbon), 95.58 (ipso-car-
bon), 165.25 (p-ring carbon), 167.22 (o-ring carbon).
MS (EI, 70 eV): m/z 198 (100, M+), 197 (31), 181 (11),
168 (17), 167 (39), 153 (12), 152 (25), 151 (34), 139 (24),
138 (26), 137 (74), 122 (16), 121 (64), 109 (14), 108 (21),
1H- and 29Si-NMR, IR, m.p, and elemental analyses
data for 1–3 are summarized in Table 1.
3.1. (2,4,6-Trimethoxyphenyl)silane, (TMP)SiH3 (1)
To a solution of (TMP)H (5.4 g, 32 mmol) in 50 ml
of THF was added n-butyllithium (14.1 ml, 2.5 M in
hexanes) with rapid stirring over 10 min. After 2 h the
solvent was removed in vacuo and the resulting off-
white solid [(TMP)Li] was washed with 100 ml of
pentane. A slurry of (TMP)Li in 80 ml of THF was
added to a cooled solution (−78°C) of SiCl4 (5.5 ml,
8.17 g, 48 mmol) in 50 ml of THF over 30 min. Several
color changes were observed from bright pink initially
to green then dark amber. After the addition was
complete, the reaction mixture was warmed to r.t. and
stirred overnight. The solvent was removed in vacuo,

56
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
107 (24), 91 (48), 90 (11), 78 (14), 77 (17), 61 (16), 59
(63). HR-MS (EI, 70 eV): Anal Calc. for C9H14O3Si
198.0712; found, 198.0711.
heated to reflux and stirred for 22 h. The resulting pale
yellow slurry was added to HSiCl3 (1.0 ml, 9.89 mmol)
in 90 ml of DME over 45 min. The reaction mixture
was stirred at r.t. for 24 h, the volatiles were removed
on a rotary evaporator, and 90 ml of Et2O were added
to the residue. To the mixture was added a slurry of
LiAlH4 (0.175g, 4.61 mmol) in 40 ml of Et2O over 20
min and the reaction mixture stirred for 24 h. After
workup with saturated NH4Cl (50 ml), the organic
layer was extracted with Et2O, dried over anhydrous
MgSO4 then filtered to give a clear pale yellow solution.
The solvent was removed on a rotary evaporator.
Purification of (TMP)2SiH2 was achieved by silica gel
column chromatography first with hexanes–Et2O (4:1)
as the eluent (to remove any (TMP)H present) followed
by Et2O to collect (TMP)2SiH2. White crystalline
(TMP)2SiH2 (2) was obtained after removal of the
solvent in 22% yield (0.84 g). No additional effort was
made to optimize the yields. Spectroscopic data for 2:
13C{1H}-NMR(C6D6): l 54.68 (p-OMe), 55.30 (o-
OMe), 91.09 (m-carbon ring), 102.01 (ipso-carbon),
164.06 (p-ring carbon), 166.99 (o-ring carbon). MS (EI,
70 eV): m/z 364 (19, M+), 348 (13), 318 (18), 303 (11),
287 (17), 271 (10), 257 (10), 241 (11), 227 (21), 211 (10),
196 (100), 181 (19), 167 (96), 152 (38), 137 (38), 121
(58), 107 (12), 91 (21), 77 (13), 59 (48).
3.2. 1-Deuterio-2,4,6-trimethoxybenzene, (TMP)D
Similar reactions of (TMP)H with n-BuLi to deter-
mine the percentage conversion to (TMP)Li were per-
formed in THF, DME, and Et2O at r.t. or at reflux
over 2–24 h. The conditions for maximum conversion
are outlined in the typical experiment described below.
To a solution of (TMP)H (0.43 g, 2.56 mmol) in 20
ml of THF was added n-butyllithium (1.2 ml, 2.5 M in
hexanes) with rapid stirring over 5 min. The reaction
was stirred at r.t. for 2 h then CD3OD (0.16 ml, 3.94
mmol) was added over 6 min. After stirring for 1.5 h,
10 ml of Et2O were added. The volatiles were removed
on a rotary evaporator, the remaining residue was
extracted with hexanes (25 ml) and filtered to give a
yellow solution. The hexane was evaporated and the
residue was dissolved in Et2O and filtered. Upon re-
moval of the solvent, (TMP)D was isolated as a white
crystalline solid (0.25 g, 94%, m.p. 51–53°C, lit. [23]
1
51–53°C). Spectroscopic data for (TMP)D: H-NMR
(CDCl3): l 3.75 (9 H, s, OMe), 6.08 (2 H, s, ArH).
13C{1H}-NMR (CDCl3): l 55.13 (OCH3), 92.50 (t,
1JCꢀD=24.6 Hz, CꢀD), 161.43 (multiplet, CꢀOMe). MS
(EI, 70 eV): m/z 169 (M+, 100), 168 (6), 140 (93), 139
(44), 126 (22), 125 (19), 110 (22), 109 (19), 108 (13), 96
(13), 95 (11), 80 (14), 79 (17), 78 (12), 69 (21), 53 (10).
3.4. Tris(2,4,6-trimethoxyphenyl)silane, (TMP)3SiH (3)
To 2,4,6-trimethoxybenzene (7.93 g, 47.2 mmol) dis-
solved in 80 ml of DME, n-butyllithium (21 ml, 51.9
mmol, 2.5 M in hexanes) was added over 15 min
followed by stirring at r.t for 3 h. A solution of HSiCl3
(0.95 ml, 9.4 mmol) in 45 ml of DME was then added
to the (TMP)H–n-BuLi solution over 10 min and the
reaction mixture stirred at r.t. for 17 h. After aqueous
3.3. Bis(2,4,6-trimethoxyphenyl)silane, (TMP)2SiH2 (2)
A solution of n-butyllithium (16 ml, 40 mmol, 2.5 M
in hexanes) was added to (TMP)H (6.08 g, 36 mmol) in
65 ml of DME over 10 min. The reaction mixture was
Table 3
Selected nonbonded distances and angles for 1–3
(TMP)SiH3 (1)
(TMP)2SiH2 (2)
(TMP)3SiH (3)
Nonbonded angles (°)
O1···Si···O3
103.4
O1…Si…O3
O1···Si···O4
O1···Si···O5
O3···Si···O4
O3···Si···O5
O4···Si···O5
103.1
81.6
163.5
106.9
60.5
O1···Si···O3
O1···Si···O4
O1···Si···O6
O1···Si···O7
O1···Si···O9
O3···Si···O4
O3···Si···O6
O3···Si···O7
O3…Si···O9
O4···Si···O6
O4···Si···O7
O4···Si···O9
O6···Si···O7
O6···Si···O9
O7···Si···O9
102.2
62.8
127.3
61.3
98.7
83.1
126.6
163.4
82.7
101.7
85.9
153.4
68.0
104.9
102.2
102.8

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
57
Table 4
Structure refinement parameters and final residual values for 1–3
1
2
3
Formula
C9H14O3Si
198.29
223 (2)
Monocliinic
P21/n
C
364.46
213 (2)
Monocliinic
P21/c
18H24O6Si
C27H34O9Si
530.63
298 (2)
Monocliinic
P21/n
Formula weight (amu)
Temperature (K)
Crystal system
Space group
Unit cell dimensions
,
a (A)
8.6072 (1)
11.3371 (2)
10.8916 (1)
90
95.824 (1)
90
1057.32 (2)
4
1.246
15.4221 (2)
16.5809 (2)
7.31360 (10)
90
94.4770 (10)
90
1864.47 (4)
4
1.298
8.22610 (10)
24.6056 (3)
13.6607 (2)
90
96.7760 (10)
90
2745.72 (6)
4
1.284
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc. (Mg m−3
)
Absorption coefficient (mm−1
Crystal size (mm)
)
0.197
0.156
0.136
0.28×0.22×0.10
2.60–26.00
−115h511
05k514
05l514
17 001
2080 (Rint=0.08)
Full-matrix least-squares on
F2
0.42×0.25×0.15
1.81–28.00
−205h520
−225k522
−95l59
17 287
0.33×0.20×0.06
1.66–24.00
−105h510
−325k532
−185l518
16 924
q range for data collection (°)
Limiting indices
Reflections collected
Independent reflections
Refinement method
4480 (Rint=0.0555)
4312 (Rint=0.0897)
Full-matrix least-squares on F2
Full-matrix least-squares on F2
Data/restraints/parameters
Goodness-of-fit on F2
2075/0/130
1.026
4467/0/234
1.068
4311/0/338
1.113
Final R indices [I\2|(I)]
R1=0.0480
wR2=0.1140
R1=0.0818
wR2=0.1312
0.230 and −0.247
R1=0.0515
wR2=0.1106
R1=0.0821
wR2=0.1247
0.400 and −0.212
R1=0.0789
wR2=0.1586
R1=0.1201
wR2=0.1778
0.349 and −0.293
R indices (all data)
Largest difference peak and hole (e
−3
,
A
)
workup with saturated NH4Cl (25 ml), the organic
layer was extracted with Et2O and the organic layer
separated and dried over anhydrous MgSO4. The solu-
tion was filtered and the solvent was removed on a
rotary evaporator. The residue was purified by silica gel
column chromatography with first 1:3 hexane–ether as
the eluent (to remove any (TMP)H present) followed by
THF to collect (TMP)3SiH. (TMP)3SiH was isolated as
a white crystalline solid in 22% yield (1.09 g). Spectro-
scopic data for 3: 13C{1H}-NMR(C6D6): l 54.62 (p-
OMe), 55.47 (o-OMe), 91.41 (m-ring carbon), 107.45
(ipso-ring carbon), 163.02 (p-ring carbon), 166.95 (o-
ring carbon). MS (EI, 70 eV): m/z 530 (0.4), 529 (0.5),
393 (41), 362 (100), 347 (20), 333 (14), 317 (14), 301
(17), 287 (11), 271 (11), 194 (11), 181 (10), 121 (11).
Bruker SMART Charge Coupled Device (CCD) Detector
system single crystal X-ray diffractometer using
graphite monochromated Mo–Ka radiation (u=
,
0.71073 A) equipped with a sealed tube X-ray source.
Preliminary unit cell constants were determined with a
set of 45 narrow frames (0.3° in 6) scans. A typical data
set consists of 4028 frames of intensity data collected
with a frame width of 0.3° in 6 and counting time of 15
s/frame at a crystal to detector distance of 4.930 cm.
The double-pass method of scanning was used to ex-
clude any noise. The collected frames were integrated
using an orientation matrix determined from the nar-
row frame scans. SMART and SAINT software packages
[24] were used for data collection and data integration.
Analysis of the integrated data did not show any decay.
Final cell constants were determined by a global refine-
ment of xyz centroids of 8192 reflections. Collected
data were corrected for systematic errors using SADABS
[25] based upon the Laue symmetry using equivalent
reflections.
3.5. X-ray structural analysis of (TMP)SiH3 (1),
(TMP)2SiH2 (2), and (TMP)3SiH (3)
Crystals of appropriate dimensions were mounted on
glass fibers in random orientations. Preliminary exami-
nations and data collections were performed using a
Crystal data and intensity data collection parameters
are listed in Table 4.

58
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 588 (1999) 51–59
Fig. 4. Partial molecular structure of (TMP)SiH3 (1), (TMP)2SiH2 (2), and (TMP)3SiH (3) showing the coordination environment around silicon
,
with the atom-labeling scheme, and nonbonded Si···O distances (A).
[2] J. Braddock-Wilking, M. Schiesher, L. Brammer, J. Huhmann,
R. Shaltout, J. Organomet. Chem. 499 (1995) 89.
[3] For recent reviews on penta- and hexacoordinated silicon com-
pounds see: (a) C. Chuit, R.J.P. Corriu, C. Reye, J.C. Young,
Chem. Rev. 93 (1993) 1371. (b) R.R. Holmes, Chem. Rev. 90
(1990) 17.
[4] (a) J.Y. Corey, C.S. John, M.C. Ohmsted, L.S. Chang, J.
Organomet. Chem. 394 (1986) 93. (b) A. Benouargha, D. Bou-
lahia, B. Boutevin, G. Caporiccio, F. Guida-Pietrasanta, A.
Ratsimihety, Phosphorus Sulfur Silicon 113 (1996) 79.
[5] J.Y. Corey, J. Braddock-Wilking, Chem. Rev. 99 (1999) 175.
[6] (a) T.D. Tilley, Comments Inorg. Chem. 10 (1990) 49. (b) J.Y.
Corey, in: G. Larson (Ed.), Advances in Silicon Chemistry, vol.
1, JAI Press, Greenwich, CT, 1991, pp. 327.
[7] See for example: (a) F.T. Edelmann, Main Group Met. Chem.
17 (1994) 67. (b) F.T. Edelmann, Comments Inorg. Chem. 12
(1992) 259.
[8] (a) M. Wada, S. Higashizaki, A. Tsuboi, J. Chem. Res. (S)
(1985) 38. (b) M. Wada, S. Higashizaki, J. Chem. Soc. Chem.
Commun. (1984) 482.
[9] (a) G. Van Koten, A.J. Leusink, J.G. Noltes, J. Organomet.
Chem. 85 (1975) 105. (b) A.J. Leusink, G. Van Koten, J.G.
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Chem. 319 (1987) C16.
Structure solution and refinement were carried out
using the SHELXTL-PLUS software package [26]. The
structures were solved by direct methods and refined
successfully in the space groups P21/n for 1 and 3 and
P21/c for 2. Full-matrix least-squares refinement was
carried out by minimizing S w(F2o−Fc2)2. The non-hy-
drogen atoms were refined anisotropically to conver-
gence. The hydrogen atoms were treated using
appropriate riding model (AFIX m3). The final residual
values and relevant structure refinement parameters are
listed in Table 4. Projection views of the molecules with
non-hydrogen atoms represented by 50% probability
ellipsoids and showing the atom labeling are presented
in Figs. 1–3. Complete listings of the atomic coordi-
nates, geometrical parameters and anisotropic displace-
ment coefficients for the non-hydrogen atoms,
positional and isotropic displacement coefficients for
hydrogen atoms are deposited with the Cambridge
Crystallographic Data Center (CCDC nos. 125736,
125737, 125738). A list of calculated and observed
structure factors is available in electronic format.
[11] E.A. Williams, in: S. Patai, Z. Rappoport (Eds.), The Chemistry
of Organic Silicon Compounds, vol. 8, Wiley, New York, 1989,
pp. 511.
Acknowledgements
[12] THF was generally used due to the cost and ease of purification.
The amount of (TMP)D formed (which represents the amount of
(TMP)Li formed) was based on mass spectral data using the
following equation: yield of (TMP)=[PD/(A+PD)]×100%
where PD is the intensity of the parent ion for (TMP)D (m/z=
169) and A is the residual protonated (TMP)H material. The
parameter A is defined as: A=(P−1)D−(P−1)H with the
subscripts referring to the deuterated (D) or protonated (H)
species. The (P−1) term refers to the (parent ion−1) peak in
the mass spectrum.
We thank the University of Missouri, St. Louis Re-
search Award for financial support, the National Sci-
ence Foundation and the University of Missouri, St.
Louis Center for Molecular Electronics for equipment
grants for The University of Missouri, St. Louis High
Resolution NMR Facility and X-ray Crystallography
Facility.
[13] C. Brelier, F. Carre, R.J.P. Corriu, M. Poirier, G. Royo, J.
Zwecker, Organometallics 8 (1989) 1831.
[14] C. Brelier, F. Carre, R.J.P. Corriu, G. Royo, M. Wong chi Man,
Organometallics 13 (1994) 307.
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